Coherent bathymetric features along the Reykjanes Ridge indicate that there were significant changes in the flux of buoyant material within the Icelandic Hot Spot during the Neogene. The radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km, and therefore these changes affected the Greenland-Scotland Ridge (GSR). At present, sill depths along the GSR are generally less than 500 m with the deepest passage being less than 1000 m, making the overflow water sensitive to even small changes in the ridge depths. Reconstructions of Neogene mantle plume activity correlate with the deepwater circulation patterns in the North Atlantic. Times of high mantle plume activity caused Northern Component Water (NCW) production to cease. NCW fluxes resumed once this phase of high mantle plume activity slowed. The long-term climate change during the Neogene must be controlled by factors other than NCW production. However, climatic optima during the late early Miocene and early Pliocene appear to have been augmented by high NCW fluxes, while subsequent middle Miocene and "middle" Pliocene coolings correlate with uplifts on the GSR and reduced NCW flux. We suggest that reductions in NCW may have contributed to both of these cooling events. Copyright 1996 by the American Geophysical Union.